Strange that you couldn't find anything on the web about valve clearances for your Suzuki GR 150. Here is what I found in about 30 seconds:
The Suzuki GR 150 valve clearance values are: Intake: 0.05 - 0.07 mm, Exhaust: 0.13 - 0.18 mm. It's crucial to check and adjust valve clearance regularly, ideally every 2000 km, on a cold engine.
Important Notes:
Check on a Cold Engine:
Valve clearances should be checked and adjusted when the engine is completely cold, as valve clearances change with temperature.
Recommended Oil Change:
Use quality synthetic engine oil and change it frequently, even if the bike is running smoothly, to prevent issues related to valve clearance, according to a post on Facebook.
Regular Maintenance:
In addition to valve clearance checks, ensure other regular maintenance tasks are performed, such as air filter cleaning and chain adjustment.
